BRK(2) Linux Programmer's Manual BRK(2)
brk, sbrk - change data segment size
int brk(void *addr);
void *sbrk(intptr_t increment);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE ||
(_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
!(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
brk() and sbrk() change the location of the program break, which defines the end of the
process's data segment (i.e., the program break is the first location after the end of the
uninitialized data segment). Increasing the program break has the effect of allocating
memory to the process; decreasing the break deallocates memory.
brk() sets the end of the data segment to the value specified by addr, when that value is
reasonable, the system has enough memory, and the process does not exceed its maximum data
size (see setrlimit(2)).
sbrk() increments the program's data space by increment bytes. Calling sbrk() with an
increment of 0 can be used to find the current location of the program break.
On success, brk() returns zero. On error, -1 is returned, and errno is set to ENOMEM.
(But see Linux Notes below.)
On success, sbrk() returns the previous program break. (If the break was increased, then
this value is a pointer to the start of the newly allocated memory). On error,
(void *) -1 is returned, and errno is set to ENOMEM.
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
Avoid using brk() and sbrk(): the malloc(3) memory allocation package is the portable and
comfortable way of allocating memory.
Various systems use various types for the argument of sbrk(). Common are int, ssize_t,
The return value described above for brk() is the behavior provided by the glibc wrapper
function for the Linux brk() system call. (On most other implementations, the return
value from brk() is the same; this return value was also specified in SUSv2.) However,
the actual Linux system call returns the new program break on success. On failure, the
system call returns the current break. The glibc wrapper function does some work (i.e.,
checks whether the new break is less than addr) to provide the 0 and -1 return values
On Linux, sbrk() is implemented as a library function that uses the brk() system call, and
does some internal bookkeeping so that it can return the old break value.
execve(2), getrlimit(2), end(3), malloc(3)
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Linux 2010-09-20 BRK(2)